[Experimental study of dynamic mechanical properties of the knee joint in varus-valgus direction in vivo]

In the present experiment an attempt was made to investigate dynamic mechanical properties of the knee in varus-valgus direction in vivo. Twelve adult cats with the knees which consist of medial collateral, lateral collateral, anterior cruciate and posterior cruciate ligaments were used. A measuring device, which was developed for this investigation, consisted of a fixation unit, a driving unit and strain and force transducers. Non-linearity of these transducers were 0.5% F.S. and 1% F.S. respectively. Both static and dynamic measurement could be performed with the measuring device. The femur of the cat was firmly clumped with the fixation unit. Care was taken to avoid crushing the skin and muscles by splitting small part of the skin and underlying muscles. Operation and measurement were carried out under general anesthesia and a muscle relaxant was given at regular intervals. Sinusoidal bending strain (bending oscillation) of 0.3, 1.0, 1.6, 3.3, 5.0, 8.6 and 10.0 Hz in varus-valgus direction was transmitted to the knee-leg complex under each pre-bending strain, which was given to varus or valgus direction prior to the initiation of the test, and bending moment was measured. Bending strain could be regarded as generated in the knee because bending strain in the femur and tibia may be ignored. Frequency, amplitude and phase of bending strain-bending moment response were analysed after passing through amplifiers and low-pass filters, and dynamic mechanical properties of the knee-leg complex was given as a complex bending elastic coefficient. Overall error of the present investigation was within 5%. Dynamic mechanical properties of the knee-leg complex resembled those of the Kelvin model on condition that pre-bending strain and amplitude of bending oscillation were constant. Corner frequency was approximately 5 Hz. It suggested that bending elastic and bending dumping coefficients of the knee were calculated by the least square method. Bending elastic and bending dumping coefficients of the knee were under the influence of pre-bending strain and amplitude of bending oscillation. As the pre-bending strain, which was loaded in the step-loading method, increased on condition of constant amplitude, bending elastic coefficient increased linearly, while bending dumping coefficient increased although the rate of increase decreased gradually. As amplitude increased sequentially from small to large on condition of constant pre-bending strain, both bending elastic and bending dumping coefficients decreased monotonously. However, dumping-elastic ratio (D/K) of the knee was approximately constant in spite of variation of those parameters.(ABSTRACT TRUNCATED AT 400 WORDS)